Japanese laid-open patent publication number 2002-328525 discloses an image forming device, such as a copier, a printer or a facsimile machine, that uses an electrographic method. The image forming device has a developing device, which supplies a developer to an electrostatic latent image formed on a latent image carrier, and develops the latent image as a developer image. Some of these kinds of developing devices use a developer in which toner contains an externally added agent such as silica in order to improve charging ability and fluidity.
However, there was a problem that, when a developing device used the aforementioned developer, in a period between when the developing device was manufactured and when the developing device is used, in other words, when the developing device is not in use, silica or the like, which is used as an externally added agent, becomes isolated from the toner. The isolated silica or the like agglomerates at a location where the feeding roller contacts the developing roller, which results in white bands appearing on the printing medium.
Hence, an object of the present application is to provide a developing device that can avoid the problem of white bands appearing on the printing medium when the externally added agent agglomerates between the feeding roller and the developing roller.